Certain aspects of the present invention, insofar as it is applied to the dewatering of pipes in order to prevent freeze-up, are related to the system disclosed in Canadian Patent No. 1,122,877, Gauthier, May 1982. Another system using air pressure in combination with a hose is by Erickson, U.S. Pat. No. 3,626,985 December 1971. This system is intended and suited for high flow rate agricultural systems with large diameter pipes, for operation in temperate climates.
Erickson employs a collapsible inner hose within his large diameter irrigation pipe, using air from an air tank to collapse the inner hose, and perforated drain tubes to ensure full fluid removal, to lighten the pipes and facilitate system relocation.
The persistence of the problems of water system pipe freeze-up appears evident from U.S. Pat. No. 5,014,731 May 1991, which employs an over-pressure responsive drain valve that is actuated by over-pressure generated by the anomalous increase in the specific volume of water when the temperature thereof drops below four degrees Fahrenheit, just prior to freeze-up taking place. The drain valve has a time delay, permitting line drainage, followed by valve closure and replacement flow of warmer water, to refill the system.
Canadian Patent No. 814,792 Cronin, June 1969 shows the use of an expansible rubber pipe within a rigid conduit, for transferring air-borne particulate material. Increased air pressure swells the inner pipe, to dislodge particulate material coated on to the inner surface of the expansible pipe, thus permitting it to be blown clear.
U.S. Pat. No. 4,662,829 May 1987, discloses an air-driven pump having an air-differential pressure chamber and an adjoining pumping chamber. The air chamber includes a mechanically displaced venting valve to cause cyclic operation of the system. The air chamber operates with either positive applied air pressure, or with negative pressure (suction).
In the case of avoiding waterline freeze-up, the two prior water displacement systems, of Erickson and Gauthier, do not appear to have become commercially viable, as the most widely used system at present appears to be that employing an electrically heated cable, such as that of the Heat-Line Corporation, or the Pyrotennax.RTM. system. The latter system presently has a cost of about $39 per meter ($12 per foot), and with rather high associated running costs for the required electrical current consumption, at about 22-watts per meter, (7-watts per foot) when active.
One of the probems that has occurred with the above referred-to Gauthier system, that may have prevented its commercial success, is the failure of its flexible-walled inner hose, where it secures to the end fitting. In use, upon repeated cycles of collapse and expansion, the thick-walled hose fails in tension. Gauthier relies upon the inherent self-restoring tendency of a thick-walled gum-rubber hose both to expand diametrically under pumping pressures, and to contract subsequently, upon cessation of pumping, so as "to provide significant dewatering of the hose on depressurization of the hose". This effect is assisted with the application of air pressure, from a residual air cushion surrounding the hose.